character inputs and linked lists

This is a discussion on character inputs and linked lists within the C Programming forums, part of the General Programming Boards category; hi, i really need help please. this code is using scanf with linked lists and the problem im mainly having ...

  1. #1
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    character inputs and linked lists

    hi, i really need help please.
    this code is using scanf with linked lists and the problem im mainly having is that if the input is more than one word eg 'hello world', it doesnt input the two words inside the array. its supposed to be reading from standard input and the 1st letter of each node is printed out. and if its a vowel, it prints out a * after the letter. heres an example of input output.

    input:
    all
    people are
    able
    to
    breathe

    output:
    a*pa*tb

    its skipping the whitespace. ive tried using getchar, but i dont know how to properly copy the characters individually into the array. i also want to keep the code as simple as possible.

    Code:
    #include<stdlib.h>
    #include<stdio.h>
    #include <string.h>
    
    typedef struct Node {
       char string;
       struct Node * next;
    }Node;
    
    int main()
    {
    	Node * curr, * head = NULL, * previous = NULL;
    	char line[100];
    	char *linep;
    	char ch;
    
    	while((scanf("%s", line)) != EOF)
    	{
    		linep = strdup(line);
    		curr = (Node *)malloc(sizeof(Node));
    		curr->string = linep[0];
    
    		if(head == NULL)
    		{
    			head = curr;
    			previous = curr;
    		}
    		else
    		previous->next  = curr;
    		previous = curr;
    	}
    
    	curr = head;
    	while(curr)
    	{
    		ch = curr->string;
    		printf("%c", ch);
    		if(ch == 'a' || ch == 'A')
    		printf("*");
    		if(ch == 'e' || ch == 'E')
    		printf("*");
    		if(ch == 'i' || ch == 'I')
    		printf("*");
    		if(ch == 'o' || ch == 'O')
    		printf("*");
    		if(ch == 'u' || ch == 'U')
    		printf("*");
    
    		curr = curr->next;
    	}
    	return(0);
    }
    cheers

  2. #2
    Beginner leiming's Avatar
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    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    
    typedef struct Node {
       char string;
       struct Node * next;
    }Node;
    
    int main()
    {
    	Node * curr, * head = NULL, * previous = NULL;
    	char line[100];
    	char *linep;
    	char ch;
    
    	while((scanf("&#37;[^\n]", line)) == 1)
    	{
    		linep = strdup(line);
    		curr = (Node *)malloc(sizeof(Node));
    		curr->string = linep[0];
    
    		if(head == NULL)
    		{
    			head = curr;
    			previous = curr;
    		}
    		else
    		previous->next  = curr;
    		previous = curr;
    		stdin->_cnt = 0;
    	}
    
    	curr->next = NULL;
    	curr = head;
    	while(curr)
    	{
    		ch = curr->string;
    		printf("%c", ch);
    		if(ch == 'a' || ch == 'A')
    		printf("*");
    		if(ch == 'e' || ch == 'E')
    		printf("*");
    		if(ch == 'i' || ch == 'I')
    		printf("*");
    		if(ch == 'o' || ch == 'O')
    		printf("*");
    		if(ch == 'u' || ch == 'U')
    		printf("*");
    
    		curr = curr->next;
    	}
    	return(0);
    }

  3. #3
    CSharpener vart's Avatar
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    better yet use fgets to read full line, and do not access members of stdin due to portability problems
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  4. #4
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    thanks for your replies, but i have tried leiming's modification, but it doesnt compile in unix gcc (because of the _cnt). and i have no idea how to use fgets

    ive thought about this tho. but the problem with this code is that if i enter 'asdf' that stores in the variable c. how do i get ONLY the first character from the input? the getchar seems the easiest method for me (i think), but i dont know how to only get the first character and ignore the rest.

    cheers

    Code:
    int main()
    {
    	Node * curr, * head = NULL, * previous = NULL;
    	char line[100];
    	char *linep;
    	char ch;
            char c;
    
    	while((c=getchar()) != EOF)
    	{
    		curr = (Node *)malloc(sizeof(Node));
    		curr->string = c;
    
    		if(head == NULL)
    		{
    			head = curr;
    			previous = curr;
    		}
    		else
    		previous->next  = curr;
    		previous = curr;
    	}

  5. #5
    Beginner leiming's Avatar
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    I'm sorry that I find my way to flush input buffer is seriously wrong.

    try this?

    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    
    typedef struct Node {
       char string;
       struct Node * next;
    }Node;
    
    int main()
    {
    	Node * curr, * head = NULL, * previous = NULL;
    	char line[100];
    	char *linep;
    	char ch;
    	char useless;
    
    	while((scanf("&#37;[^\n]%c", line, &useless)) >= 2) /* %c to "eat" the '\n' */
    	{
    		linep = strdup(line); /* by the way, I can't make sure if it's necessary to "free(linep)" ? */
    		curr = (Node *)malloc(sizeof(Node));
    		curr->string = linep[0];
    		/* free(linep); */
    		if(head == NULL)
    		{
    			head = curr;
    			previous = curr;
    		}
    		else
    		previous->next  = curr;
    		previous = curr;
    	}
    
    	curr->next = NULL;
    	curr = head;
    	while(curr)
    	{
    		ch = curr->string;
    		printf("%c", ch);
    		if(ch == 'a' || ch == 'A')
    		printf("*");
    		if(ch == 'e' || ch == 'E')
    		printf("*");
    		if(ch == 'i' || ch == 'I')
    		printf("*");
    		if(ch == 'o' || ch == 'O')
    		printf("*");
    		if(ch == 'u' || ch == 'U')
    		printf("*");
    
    		curr = curr->next;
    	}
    	return(0);
    }
    Last edited by leiming; 05-25-2008 at 06:18 AM.

  6. #6
    and the hat of wrongness Salem's Avatar
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    Use
    while ( fgets( line, sizeof line, stdin ) != NULL )

    and this whole "flush the buffer" thing goes away. Dealing with a newline in a char array is far simpler than any kind of "flush input" hack you can come up with.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
    CSharpener vart's Avatar
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    /* &#37;c to "eat" the '\n' */
    to eat input use * in scanf format
    for example

    %*c - and you do not need any useless variables

    PS. I'm not talking about this very case - Salem's solution is enough
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
    Beginner leiming's Avatar
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    Quote Originally Posted by vart View Post
    to eat input use * in scanf format
    for example

    &#37;*c - and you do not need any useless variables

    PS. I'm not talking about this very case - Salem's solution is enough
    I find a problem with * in scanf format.
    BCC thinks this is a successfully read one while GCC not.

    Quote Originally Posted by Salem View Post
    Use
    while ( fgets( line, sizeof line, stdin ) != NULL )

    and this whole "flush the buffer" thing goes away. Dealing with a newline in a char array is far simpler than any kind of "flush input" hack you can come up with.
    Excuse me, why did I find fgets returns an array {'\n', '\0'} instead of NULL when an empty line is got?
    Is there anything wrong with my operation?
    Thanks.
    Last edited by leiming; 05-25-2008 at 06:03 PM.

  9. #9
    Registered User ssharish2005's Avatar
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    >Excuse me, why did I find fgets returns an array {'\n', '\0'} instead of NULL when an empty line is got?

    Leiming, thats how the fgets has been implemented. It reads the whole content of the input buffer including the '\n' char, which the scanf does leave them in the input buffer, which then causes lots of problem in the future, when using any operation which needs to access-the standard input. If your using fgets then its obvious that you need to eliminate the '\n' char from the vector by using the strchar and replacing it with the '\0'.

    Pleas read one of our FAQ about, how to read string from the user or something. Which explains the complete usage of fgets and internal working mechanisms.

    ssharish

  10. #10
    CSharpener vart's Avatar
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    BCC thinks this is a successfully read one while GCC not.
    get rid of bcc?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  11. #11
    Beginner leiming's Avatar
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    >>ssharish2005

    Thanks for your explaining.

    But I knew this before. Maybe I didn't express myself clearly. (Sorry to not learn English well)
    I mean, an empty line couldn't end the loop if using Salem's code.
    Or I didn't got it how people usually do to show that the input is over.

    By the way, I have tried to use his code again just now and found that pressing "Ctrl + Z" and then pressing "Enter" could make fgets return NULL.

    LeiMing

    by the way, I writes no code in this post but when I quotes your post then posts it it forces me to use code tag. How to deal with it correctly?

  12. #12
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    thx for all your replies. i was just wondering, is there any way to implement this with getchar() and getting only the first letter of the input like my previous post? i just feel that this exercise is better to use with getchar() != EOF. but when i use getchar() it returns the whole input. i only want the first letter.

    cheers

  13. #13
    Registered User ssharish2005's Avatar
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    Quote Originally Posted by zomg View Post
    thx for all your replies. i was just wondering, is there any way to implement this with getchar() and getting only the first letter of the input like my previous post? i just feel that this exercise is better to use with getchar() != EOF. but when i use getchar() it returns the whole input. i only want the first letter.

    cheers
    Zomg, its not an efficient way of doing this with the getchar. That takes too much code and perhaps you will have to read stuff char by char and then append it the string. See the following code for the fgets usage.

    Code:
    #include <stdio.h>
    int main()
    {
        char cont[25];
        char *ptr;
        
        while( fgets( cont, sizeof cont, stdin) != NULL )
        {
               if( ( ptr = strchr( cont, '\n' ) ) != NULL )
                   *ptr = '\0';
               printf( cont ); 
               
               /* Here, fill you structure data members
                  by the string which is read above. Use
                  strcpy function to copy it onto structure
                  memeber */
        }
        return 0;
    }
    NOTE: You will have press Clt + Z. To stop reading values from user.

    ssharish

  14. #14
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    awsome. there is just one more thing i would like to ask. well atm my uni website is actually testing the code, and its not passing every test. i think its actually of one thing: how do i make it do nothing, if there is no input. eg if i just press enter, how do i make it do nothing, instead of making it allocate a element with a space? atm its actually placing a space inside the element and i think its meant to do nothing.

    cheers

  15. #15
    Registered User ssharish2005's Avatar
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    Quote Originally Posted by zomg View Post
    awsome. there is just one more thing i would like to ask. well atm my uni website is actually testing the code, and its not passing every test. i think its actually of one thing: how do i make it do nothing, if there is no input. eg if i just press enter, how do i make it do nothing, instead of making it allocate a element with a space? atm its actually placing a space inside the element and i think its meant to do nothing.

    cheers
    Ok, what you need to do is to check the first element in the string and see if its a '\n' char. If it, then you know that the user had has entered nothing. From there on, you either exit the code or come out of the loop and so something else. Few points to hightlight

    1. Check the first element in the string
    2. If that element is '\n'
    3. Then user entered nothing

    Hope you get that part.

    ssharish

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